In known high pressure, high temperature systems where a pump is operating with a fluid which has undesirable characteristics especially to motors, mechanical seal assemblies are employed to separate two fluid zones. A buffer fluid, generally the same fluid as used in the motor environment having a pressure above product pressure and a temperature generally less than product temperature is supplied from a constant flow source to the O.D. of the seal. The supply of the buffer fluid being substantially constant, a by-pass means is generally provided in parallel with the seal. The constant flow source is employed because with a product pressure, as on the order of 3000 p.s.i., pressure control is difficult, expensive and a source of unreliability.
Upon failure of the buffer fluid source, the seal is pressurized at the I.D., potentially at full product pressure, such that the abutting seal faces of the seal are subjected to tensile stresses which could lead to fracture of the seal rings. This leads to failure of the seal and the flow of product with its undesirable characteristics to the motor.